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authorEric Dumazet <dada1@cosmosbay.com>2008-11-24 16:07:50 -0800
committerDavid S. Miller <davem@davemloft.net>2008-11-24 16:07:50 -0800
commita21bba945430f3f5e00c349665f88cdacdb32a8d (patch)
tree9ff6a910b16925d2ee3c02b7221f3984ad5cd949
parent2e77d89b2fa8e3f8325b8ce7893ec3645f41aff5 (diff)
net: avoid a pair of dst_hold()/dst_release() in ip_push_pending_frames()
We can reduce pressure on dst entry refcount that slowdown UDP transmit path on SMP machines. This pressure is visible on RTP servers when delivering content to mediagateways, especially big ones, handling thousand of streams. Several cpus send UDP frames to the same destination, hence use the same dst entry. This patch makes ip_push_pending_frames() steal the refcount its callers had to take when filling inet->cork.dst. This doesnt avoid all refcounting, but still gives speedups on SMP, on UDP/RAW transmit path. Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv4/ip_output.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 5516825a0751..8ebe86dd72af 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1284,7 +1284,12 @@ int ip_push_pending_frames(struct sock *sk)
skb->priority = sk->sk_priority;
skb->mark = sk->sk_mark;
- skb->dst = dst_clone(&rt->u.dst);
+ /*
+ * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
+ * on dst refcount
+ */
+ inet->cork.dst = NULL;
+ skb->dst = &rt->u.dst;
if (iph->protocol == IPPROTO_ICMP)
icmp_out_count(net, ((struct icmphdr *)